The proposed research involves the development of new methods to determine site to site distances on biological macromolecules and assemblies using small angle x-ray scattering methods. The primary application of these methods will be to obtain high resolution structural information about the acetylcholine receptor from Torpedo Californica. Metal ions (terbium and mercury) attached to various components of the receptor will be used to "visualize" that the location of specific sites relative to each other or to other electron density such as a membrane bilayer. This will be accomplished using the anomalous scattering power of an element when the incident wavelength is very near a L2 or L3 absorption edge of the element. Synchrotron radiation will be used as the tunable, intense x-ray source for these experiments. Studies of the acetylcholine receptor in various states should yield information on subunit organization and perhaps lend insight into how the receptor acts as an ion gate. Finally, parallel theoretical work will be done on new mathematical mechanics to angle scattering data and to investigate the use of statistical mechanics to understand forces in protein-lipid bilayer interactions.